As used herein, the term "magnetic" refers to particles which are magnetically susceptible, and is not meant to necessarily imply particles which are themselves permanently magnetized. The invention concerns an apparatus for the removal of such particles from particle mixtures containing both magnetic and non-magnetic particles. Such procedures are typically used in association with iron mining operations, for example in instances in which the ore is of relatively low grade and contains much extraneous rock material, or gangue. An example of such an operation is a typical oxidized taconite mining operation, wherein the ores are relatively low grade and contain primarily weakly magnetic iron minerals as the primary magnetic component. Such ores are generally of no better quality than the discarded "tailings" of many iron mining operations, and indeed tailings from mining operations may become a valuable source of iron, due to use of a separator such as that described herein. The tailings, with magnetic materials removed, may also have commercial value.
Separation of solids according to their magnetic properties is well-known, and devices are known to perform this function. Such devices are described in detail in U.S. Pat. Nos. 3,947,349 and 4,046,680, the disclosures of which are incorporated herein by reference. Both patents issued to the inventor of the present patent, and generally concern high intensity separators. Such separators are known to perform the separation function on either wet and dry particles (slurries or powders). Further, the devices are quite effective for the recovery of weakly magnetic particles. The present invention concerns substantial improvements to such devices, yielding the advantages described herein. Generally, these relate to enablement of use of a relatively fine, high density, matrix for excellent magnetic pick up. Such a matrix could not previously be utilized as effectively, for reasons that will be apparent from the descriptions.
The conventional devices generally each comprise a large rotatable drum having a series of parallel, circular, races through which ore material to be separated is directed. Each race is generally filled with a matrix material. As the drum is rotated, the races are concurrently rotated through a 360.degree. arc. Through a portion of the arc of rotation, the matrix material in each race is passed through an applied magnetic field. During this portion of arc movement, magnetically susceptible or magnetic materials within the ore become entrapped within the mesh. The non-magnetic materials, however, are unaffected by the magnetic field and are free to move and pass outwardly from the mesh material even within the magnetic field. The weakly magnetic materials can be released from the mesh material, after the mesh material passes beyond the applied magnetic field.
A typical operation, then, concerns appropriate direction of feed stock input into each race, relative to the applied magnetic field. Generally, the ore material is directed into the race immediately preceding, or during, rotation of the race through the applied magnetic field. Once the ore material is introduced to the race, and the race is passed into the magnetic field, the magnetic components begin to become attached to and entrapped within the mesh. Non-magnetic portions, however, pass through the mesh and outwardly from the race. Continued rotation of the race brings the mesh and entrapped magnetic material beyond the magnetic field, and the magnetic components are released from the mesh and are washed out of the race. Separate collectors can be positioned and used to receive the magnetics and non-magnetics independently. Circular construction of the individual races permits efficient operation as a continuous, rather than a batch, system. Again, this is described in detail in the '349 and '680 patents, referenced above.
While the above described systems work well in some applications, they are not completely satisfactory. Separation could be improved if finer mesh screens could be used in the races. Also, improved control of flow through the mesh would achieve improved performance.